1. Field of the Invention
The present invention relates to a callback mechanism between two telecommunication terminals one of which is a wireless telephone and, more particularly, to data communication between a data server in a local area network and a wireless telephone which can not autonomously accept a call for establishing callback connection.
2. Description of the Related Art
There is a system for callback communication between a wireless telephone and a data server. The wireless telephone, which is provided as terminal equipment of digital cordless telecommunication system, PDC (personal digital cellular telecommunication system) or the like, sends a request for data to the data server. The data server calls the wireless telephone to send the requested data to the wireless telephone. In order to receive the data, the wireless telephone should accept the call autonomously.
For example, there is a PBX (private branch exchange) system to which PHS (personal handy phone system) is applied. In the PBX system, a TA (terminal adapter) is installed at an output point (T point) of a DSU (digital service unit) connected with ISDN (integrated services digital network). At output R points of the TA, a base station and other data terminals are connected with the TA. The base station is connected with terminals by a wireless path or channel. With this structure, the terminals are put into a state of accepting callback from the base station autonomously.
General wireless telephones, however, are not always installed with a function for accepting callback. If a wireless telephone without such a function is used as a terminal of the above-mentioned PBX system, the wireless telephone cannot accept callback from the data server.
Moreover, when the terminal is not given an identifier for specifying each of the terminals connected with the base station, the base station cannot select one of the terminals for sending callback so that the terminal can not receive the callback, even if the terminal is available for callback.
Description will be made about a callback communication procedure of a practical wireless PBX system whose terminals are not given their identifiers with reference to FIG. 1. The system comprises a data server, a base station and plural wireless terminals. First, one of the terminals sends a request for callback to the base station by wireless path (STEP 1). Next, the base station sends the request to the data server by a wired line (STEP 2). The request of STEP 2 includes a telephone number of the base station, but does not include the identifier of the terminal. Consequently, even if the data server sends callback back to the base station (STEP 3), the base station cannot relay the callback to the terminal.